The dynamics of soil moisture distribution and thawingfreezing process of stipa steppe in central Mongolia during the seasonal transition period (2003~2004) were analyzed with the measurement of temperature and moisture in the soil profile combined with the meteorological data. The results show that there is a completely frozen period about 154~ 160 d in the soil profile of 0~150 cm. The diurnal freeze/thaw cycle mainly takes place at the ground surface of 0~ 5 cm. The soil moisture in 0~30 cm layer changes intensively in the thawingfreezing processes, as well as the soil temperature. In general, the soil water content at 10 cm depth is always higher than those of other depths. The seasonal variation of soil moisture weakened gradually with the increasing soil depth. The frozen soil is favor of keep water, which benefits the regreening of grass in spring.